In multiple-user gas systems of the type having a plurality of users each of which is operating a separate although usually identical gas using apparatus, problems can occur when any one of those independent users either suddenly discontinues use, or if such a user was not previously using gas suddenly begins use. More specifically, an example of a multiple-user gas system would be a multiple station air operated spray painting system. In such a system each of a plurality of spray paint operators has a hand held air atomized spray gun, each gun of which is connected to a central or common air source. The problem occurs when any one of those operators either discontinues use or begins use of a gun that was not previously in use. The conventional supply/shut-off device provided at each of the air operated paint spray guns in a multiple-user system simply turns-on or turns-off the air supply without any consideration of the other operators. In a compressible gas system the volume of gas maintained in the lines to each of the multiple users from the common source will suffer either a pressure increase spike when use is discontinued or a sudden pressure decrease at the moment when use of a previously unused nozzle is commenced. This pressure increase or decrease is only a momentary occurence since the system is a flow system and each of the guns in use will quickly bleed off the excess pressure or the central air supply unit will make up the defficiency in pressure thereby overcoming the spike or dip, depending upon what has occurred. However, during that momentary pressure increase or decrease, the delicate balance between air usage and paint usage is interrupted. If there is a pressure increase the paint spray guns remaining in use will over-atomize the paint thereby causing "over-spray", which will result in an improper paint job or if a momentary pressure decrease occurs there will be under-atomization for a short period of time on the remaining nozzles resulting in paint globules of too large a size. Either of these conditions results in an improper paint job and heretofore there has been no practical method of solving such a problem, manufacturers and spray paint operators simply having learned to live with the problem.
Therefore, there is a need for an improved supply/shut-off device specifically for use in a multiple-user gas system of the previously described type that will allow for any one of the multiple gas users to either discontinue or to re-commence use of his gas using machine.